separate out mathematical constants

...to allow distinguishing stuff like Euler's number from variable name `e`

src/math.jl

@@ -23,8 +23,10 @@ This attempts to parse out a decent Julia-esque ([`Math`](@ref) AST from a
 pointer to `ASTNode_t`.
 """
 function parse_math(ast::VPtr)::Math
-    if ast_is(ast, :ASTNode_isName) || ast_is(ast, :ASTNode_isConstant)
+    if ast_is(ast, :ASTNode_isName)
         return MathIdent(get_string(ast, :ASTNode_getName))
+    elseif ast_is(ast, :ASTNode_isConstant)
+        return MathConst(get_string(ast, :ASTNode_getName))
     elseif ast_is(ast, :ASTNode_isInteger)
         return MathVal(ccall(sbml(:ASTNode_getInteger), Cint, (VPtr,), ast))
     elseif ast_is(ast, :ASTNode_isReal)

src/structs.jl

@@ -74,6 +74,14 @@ struct MathIdent <: Math
     id::String
 end
 
+"""
+A constant identified by name (usually something like `pi`, `e` or `true`) in
+mathematical expression
+"""
+struct MathConst <: Math
+    id::String
+end
+
 """
 Function application ("call by name", no tricks allowed) in mathematical expression
 """